1. Field of the Invention
This invention relates generally to systems and methods for monitoring blood constituents, and in particular, to improved methods and systems for integrating a blood monitoring system with a vascular sampling system for periodically measuring blood analytes and parameters using electrochemical, photochemical, optical techniques or a combination of the above techniques.
2. Description of Related Art
Tight glycemic control has been associated with better clinical outcomes in critical care settings. There are a number of inventions devoted to sampling, measuring, and/or regulating blood glucose levels of patients in ICU and undergoing surgery. The inventions comprising this field generally perform one or more of these functions independently or in a few cases integrate with other devices to provide a closed loop composite system that regulates blood glucose. This field is teeming with improvements by the inventors who are generally groups of professional engineers and physicians, constantly attempting to design improvements to the prior art in order to innovate a system that hospitals and physicians will embrace widely. Heretofore, none of the so called “closed loop” systems, which sample, measure, and administer medicine to adjust blood glucose levels, enjoy popular use. As will be pointed out below, many problems with the prior art are to blame.
Generally speaking the relevant prior art inventions are complex, cumbersome, expensive, and risky to use (i.e. detrimental to the health of the patient). To enjoy pervasive use by the medical community, irrespective of the techniques and tools used by the artisan, the ideal system for blood glucose regulation of ICU and surgery patients must be simple and convenient to use by medical teams. The ideal system must have a low cost of ownership to the hospitals. And most importantly, the ideal system must not aggravate or compromise the health of the vulnerable patients in the OR or ICU.
One of the biggest problems with prior art automated blood sampling is clotting. To deal with the problem U.S. Patent 2007/0191716, titled Blood Monitoring System, to Goldberger et. al. has suggested the use of warfarin and heparin as an IV flush solution. Warfarin has several limitations such as it can only be given orally and not as an IV flush solution; it interacts with many commonly used medications; and frequent monitoring is required to ensure a safe dose is taken. While, natural heparin has been a commonly used anti-coagulant for IV flush solutions, its safety has been questioned for several reasons, particularly due to the potential risk of heparin induced thrombocytopenia (HIT).
A common problem plaguing the prior art is infection induced by system components and chemicals contacting re-infused blood. Pumps, valves, and sensors tend to accumulate impurities in crevices, which can contaminate bodily fluids. This is common with syringe pumps, air pumps and stop-cocks, which are typical prior art components. A typical technique for grappling with the problem is to use separate passageways for bodily fluids and medications, as in U.S. Patent Application 2006/0188407 titled Fluid handling cassette having a spectroscopic sample cell, to Gable, et al. The spectroscopic measurement method disclosed in this application requires the use of a centrifuge module that separates plasma from the blood sample for being able to perform reliable measurement. Furthermore, the system uses an extensive tubing network, and requires multiple pumps, valves and sensors, thus increasing the overall complexity and costs of producing and maintaining such systems. Another example is U.S. Patent Application 2007/0239096, titled Anti-clotting apparatus and methods for fluid handling system, to Keenan et al. This anti-clotting apparatus is restricted to a method of intermittently providing anti-clotting agents and the transmission of ultrasonic energy to a passageway of the blood flow system. The system additionally requires the use of potentially unsafe anionic detergents to clear the passageways.
Another typical problem inherent in the field is that the systems tend to draw large quantities of blood, as in the Goldberger et. al. patent. Peripheral edema is one of several complications that can ensue from drawing and reinfusing large quantities of blood. Typical prior art systems use large bore tubing, which increases the amount of blood drawn in each cycle. For example, U.S. Patent Application 2008/0097288, titled Disposable blood glucose sensor with internal pump, to Levin et al, discloses an apparatus and method for automatically and periodically measuring the level of a patient's blood glucose when a patient has a catheter inserted in a blood vessel. The system requires the drawing and reinfusion of a large volume (2 ml) of blood for each measurement, with 200 μL being used up and the cycle having to be repeated every 60 seconds to prevent clotting. U.S. Patent Application 2008/0014601 to Goldberger et. al. suggests use of test strips based on the enzyme-glucose oxidase (GOD). GOD based strips are only suitable for measuring glucose in capillary blood derived from finger-sticks. They are not suitable for venous or arterial blood glucose measurements, due to the different oxygenation content in these blood matrices.
Another common problem in the field is controlling flush solutions with the help of gravity. Hospitals have moved away from gravity based controls, because the flow-rate cannot be precisely controlled and there is risk of excess saline being infused into the patient. Issues with accuracy of measurements and reliability of systems over protracted use plague the field. Poor sensor quality and sensor technique, as mentioned, is usually to blame. To enhance measurement accuracy U.S. Pat. No. 7,367,942, to Grage et al., requires a isolatable test chamber or side channel for the blood sample during measurement, so that there is no change in the diffusion gradient, when the blood sample is in contact with the flow-through sensor. U.S. Patent Application 2007/0225675, titled Blood Analyte Determinations, to Robinson et al, discloses methods and apparatuses to provide measurement of glucose and other analytes with a variety of sensors without many of the performance degrading problems of conventional approaches. However, as is typical of the prior art, the system requires the use of more than one pump, several valves, and a complicated tubing network. Additionally, in all prior art systems, the patient cannot be quickly and aseptically connected or disconnected from the system.
Given the state of the prior art, the present invention has various objects:    An object of the present invention is to develop a very simple but innovative system; i.e., simple and economical to make, use, and operate;    Another object is to develop a system that performs reliable automated blood sampling;    Another object is to develop a system that can operate for at least three days continuously without any human intervention when using a peripheral IV catheter;    Another object is to develop a system that effectively prevents clotting and keeps the blood passageways clear without aggravating the health of the patient;    Another object is to develop a system that has a specially designed connector to mate with the catheter hub such that the dead volume in the catheter is eliminated and the potential for thrombus formation is further minimized;    Another object is to develop a system that enables quick, aseptic connection and disconnection between the patient and the system, allowing for easy system maintenance and quick disassociation between the patient and the monitoring system for mobility;    Another object is to develop a system that utilizes a modular design such that it can be integrated with almost any kind of sensor system, including: multi-analyte flow through systems, “needle” type glucose sensors implanted in the lumen, or disposable test strips;    Another object is to develop a system that utilizes an innovative test strip feeder design and assembly that integrates with the sampling platform and allows for reliable and fully automated measurements with conventional glucose meters and test strips;    Another object is to develop a system that has a point of sampling that is not restricted to the peripheral vein, but also includes the sampling from the arterial line and central venous system;    Another object is to develop a system that is configurable to operate automatically for any length of time by the appropriate site of blood sampling, a clot-free method of sampling, micro-volume extraction of blood, and the ability to keep the veins open between sampling cycles;    Another object is to develop a blood sampling system that can also operate without the need for “reinfusion” of blood back into the patient;    Another object is to develop a system that allows a simple and reliable way to carry out therapeutic intervention based on the concentration of the blood analyte.
Therefore, in light of the foregoing, it would be further appreciated to develop a reliable blood sampling and analyzing system: simple to make, simple to use, and inexpensive to the end user; that makes use of clot-prevention techniques without compromising on the health of the patient; that uses a technique for keeping veins open during stand-by mode; that makes use of a quick aseptic connect/disconnect; that makes use of a special luer connector that mates with the catheter hub to eliminate the dead volume while also effectively reducing the chances of thrombus formation in the catheter; that employs a single blood-passageway such that the medication (insulin, dextrose, etc) and blood share the same passageway; that simplifies operations and improves overall quality of care; and that incorporates an innovative system design enabling the automated blood sampling platform to be integrated with a wide range of sensor technologies.